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Membrane Lipids (membrane + lipid)
Terms modified by Membrane Lipids Selected AbstractsDynamic organization of lymphocyte plasma membrane: lessons from advanced imaging methodsIMMUNOLOGY, Issue 1 2010Dylan M. Owen Summary Lipids and lipid domains are suggested to play an essential role in the heterogeneous organization of the plasma membrane in eukaryotic cells, including cells of the immune system. We summarize the results of advanced imaging and physical studies of membrane organization with special focus on the plasma membrane of lymphocytes. We provide a comprehensive up-to-date view on the existence of membrane lipid and protein clusters such as lipid rafts and suggest research directions to better understand these highly dynamic entities on the surface of immune cells. [source] Structural characterization of N -lignoceroyl (C24:0) sphingomyelin bilayer membranes: a re-evaluationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Hiroshi Takahashi Sphingomyelin (SM) is a membrane lipid and plays important roles in signaling, protein trafficking, cell growth and death. The structure of the bilayer of a hydrated highly asymmetric SM, N -lignoceroyl (C24:0) SM, has been investigated with X-ray diffraction (XRD), simultaneous small-angle X-ray scattering (SAXS), wide-angle XRD and SAXS. At temperatures between two endothermic transitions of hydrated C24:0 SM bilayers, the C24:0 SM formed a ripple phase with the ripple periodicity of ~12,14,nm. At about three months incubation at 277,K, the formation of a stable phase with a short lamellar spacing of 5.62,nm was induced. Based upon the structures revealed by this study and the phase behavior, intermolecular interactions between C24:0 SM molecules in the bilayer membrane are discussed. [source] The ,-amyloid protein of Alzheimer's disease binds to membrane lipids but does not bind to the ,7 nicotinic acetylcholine receptorJOURNAL OF NEUROCHEMISTRY, Issue 6 2007David H. Small Abstract Accumulation of the amyloid protein (A,) in the brain is an important step in the pathogenesis of Alzheimer's disease. However, the mechanism by which A, exerts its neurotoxic effect is largely unknown. It has been suggested that the peptide can bind to the ,7 nicotinic acetylcholine receptor (,7nAChR). In this study, we examined the binding of A,1-42 to endogenous and recombinantly expressed ,7nAChRs. A,1-42 did neither inhibit the specific binding of ,7nAChR ligands to rat brain homogenate or slice preparations, nor did it influence the activity of ,7nAChRs expressed in Xenopus oocytes. Similarly, A,1-42 did not compete for ,-bungarotoxin-binding sites on SH-SY5Y cells stably expressing ,7nAChRs. The effect of the A,1-42 on tau phosphorylation was also examined. Although A,1-42 altered tau phosphorylation in ,7nAChR-transfected SH-SY5Y cells, the effect of the peptide was unrelated to ,7nAChR expression or activity. Binding studies using surface plasmon resonance indicated that the majority of the A, bound to membrane lipid, rather than to a protein component. Fluorescence anisotropy experiments indicated that A, may disrupt membrane lipid structure or fluidity. We conclude that the effects of A, are unlikely to be mediated by direct binding to the ,7nAChR. Instead, we speculate that A, may exert its effects by altering the packing of lipids within the plasma membrane, which could, in turn, influence the function of a variety of receptors and channels on the cell surface. [source] Ethanol inhibits cold-menthol receptor TRPM8 by modulating its interaction with membrane phosphatidylinositol 4,5-bisphosphateJOURNAL OF NEUROCHEMISTRY, Issue 1 2007Jan Benedikt Abstract Ethanol has opposite effects on two members of the transient receptor potential (TRP) family of ion channels: it inhibits the cold-menthol receptor TRPM8, whereas it potentiates the activity of the heat- and capsaicin-gated vanilloid receptor TRPV1. Both thermosensitive cation channels are critically regulated by the membrane lipid, phosphatidylinositol 4,5-bisphosphate (PIP2). The effects of this phospholipid on TRPM8 and TRPV1 are also functionally opposite: PIP2 is necessary for the activation of TRPM8 but it constitutively inhibits TRPV1. This parallel led us to investigate the possible role of PIP2 in the ethanol-induced modulation of rat TRPM8, heterologously expressed in HEK293T cells. In this study, we characterize the effects of ethanol (0.1,10%) on whole-cell currents produced by menthol and by low temperature (< 17°C). We show that the inclusion of PIP2 in the intracellular solution results in a strong reduction in the ethanol-induced inhibition of menthol-evoked responses. Conversely, intracellular dialysis with anti-PIP2 antibody or with the PIP2 scavenger, poly l -lysine, enhanced the ethanol-induced inhibition of TRPM8. A 20 min pre-incubation with wortmannin caused a modest decrease in inhibition produced by 1% ethanol, indicating that the ethanol-induced inhibition is not mediated by lipid kinases. These findings suggest that ethanol inhibits TRPM8 by weakening the PIP2,TRPM8 channel interaction; a similar mechanism may contribute to the ethanol-mediated modulation of some other PIP2 -sensitive TRP channels. [source] The polyphenol epigallocatechin-3-gallate affects lipid rafts to block activation of the c-Met receptor in prostate cancer cellsMOLECULAR CARCINOGENESIS, Issue 8 2010Damian Duhon Abstract The HGF/c-Met pathway is an important regulator of signaling pathways responsible for invasion and metastasis of most human cancers, including prostate cancer. Exposure of DU145 prostate tumor cells to HGF stimulates the PI3-kinase and MAPK pathways, leading to increased scattering, motility, and invasion, which was prevented by the addition of EGCG. EGCG acted at the level of preventing phosphorylation of tyrosines 1234/1235 in the kinase domain of the c-Met receptor without effecting dimerization. HGF-induced changes were independent of the formation of reactive oxygen species, suggesting that EGCG functioned independent of its antioxidant ability. ECG, another tea polyphenol, was as effective as EGCG, while EGC and EC were less effective. EGCG added up to 4,h after the addition of HGF still blocked cell scattering and reduced the HGF-induced phosphorylation of c-Met, Akt, and Erk, suggesting that EGCG could act both by preventing activation of c-Met by HGF and by attenuating the activity of pathways already induced by HGF. HGF did not activate the MAPK and PI3-K pathways in cells treated with methyl-,-cyclodextrin (mCD) to remove cholesterol. Furthermore, subcellular fractionation approaches demonstrated that only phosphorylated c-Met accumulated in Triton X-100 membrane insoluble fractions, supporting a role for lipid rafts in regulating c-Met signaling. Finally, EGCG treatment inhibited DiIC16 incorporation into membrane lipid ordered domains, and cholesterol partially inhibited the EGCG effects on signaling. Together, these results suggest that green tea polyphenols with the R1 galloyl group prevent activation of the c-Met receptor by altering the structure or function of lipid rafts. © 2010 Wiley-Liss, Inc. [source] Importance of Interaction between C1 Domain and Lipids in Protein Kinase C, Activation: Hydrophobic Side Chain Direction in Isobenzofuranone Ligands Controls Enzyme Activation LevelCHEMMEDCHEM, Issue 7 2007Go Hirai Dr. Substituent direction is important: Type A,D isobenzofuranone derivatives were synthesized with differently directed hydrophobic alkyl side chains. These ligands bind in a similar conformation to protein kinase C, but have contrasting activation abilities, possibly owing to different interaction of the side chain with the membrane lipid. [source] Detection of microbial biomass by intact polar membrane lipid analysis in the water column and surface sediments of the Black SeaENVIRONMENTAL MICROBIOLOGY, Issue 10 2009Florence Schubotz Summary The stratified water column of the Black Sea produces a vertical succession of redox zones, stimulating microbial activity at the interfaces. Our study of intact polar membrane lipids (IPLs) in suspended particulate matter and sediments highlights their potential as biomarkers for assessing the taxonomic composition of live microbial biomass. Intact polar membrane lipids in oxic waters above the chemocline represent contributions of bacterial and eukaryotic photosynthetic algae, while anoxygenic phototrophic bacteria and sulfate-reducing bacteria comprise a substantial amount of microbial biomass in deeper suboxic and anoxic layers. Intact polar membrane lipids such as betaine lipids and glycosidic ceramides suggest unspecified anaerobic bacteria in the anoxic zone. Distributions of polar head groups and core lipids show planktonic archaea below the oxic zone; methanotrophic archaea are only a minor fraction of archaeal biomass in the anoxic zone, contrasting previous observations based on the apolar derivatives of archaeal lipids. Sediments contain algal and bacterial IPLs from the water column, but transport to the sediment is selective; bacterial and archaeal IPLs are also produced within the sediments. Intact polar membrane lipid distributions in the Black Sea are stratified in accordance with geochemical profiles and provide information on vertical successions of major microbial groups contributing to suspended biomass. This study vastly extends our knowledge of the distribution of complex microbial lipids in the ocean. [source] Quantitative modeling of triacylglycerol homeostasis in yeast , metabolic requirement for lipolysis to promote membrane lipid synthesis and cellular growthFEBS JOURNAL, Issue 22 2008Jürgen Zanghellini Triacylglycerol metabolism in Saccharomyces cerevisiae was analyzed quantitatively using a systems biological approach. Cellular growth, glucose uptake and ethanol secretion were measured as a function of time and used as input for a dynamic flux-balance model. By combining dynamic mass balances for key metabolites with a detailed steady-state analysis, we trained a model network and simulated the time-dependent degradation of cellular triacylglycerol and its interaction with fatty acid and membrane lipid synthesis. This approach described precisely, both qualitatively and quantitatively, the time evolution of various key metabolites in a consistent and self-contained manner, and the predictions were found to be in excellent agreement with experimental data. We showed that, during pre-logarithmic growth, lipolysis of triacylglycerol allows for the rapid synthesis of membrane lipids, whereas de novo fatty acid synthesis plays only a minor role during this growth phase. Progress in triacylglycerol hydrolysis directly correlates with an increase in cell size, demonstrating the importance of lipolysis for supporting efficient growth initiation. [source] Membrane binding of SRP pathway components in the halophilic archaea Haloferax volcaniiFEBS JOURNAL, Issue 7 2004Tovit Lichi Across evolution, the signal recognition particle pathway targets extra-cytoplasmic proteins to membranous translocation sites. Whereas the pathway has been extensively studied in Eukarya and Bacteria, little is known of this system in Archaea. In the following, membrane association of FtsY, the prokaryal signal recognition particle receptor, and SRP54, a central component of the signal recognition particle, was addressed in the halophilic archaea Haloferax volcanii. Purified H. volcanii FtsY, the FtsY C-terminal GTP-binding domain (NG domain) or SRP54, were combined separately or in different combinations with H. volcanii inverted membrane vesicles and examined by gradient floatation to differentiate between soluble and membrane-bound protein. Such studies revealed that both FtsY and the FtsY NG domain bound to H. volcanii vesicles in a manner unaffected by proteolytic pretreatment of the membranes, implying that in Archaea, FtsY association is mediated through the membrane lipids. Indeed, membrane association of FtsY was also detected in intact H. volcanii cells. The contribution of the NG domain to FtsY binding in halophilic archaea may be considerable, given the low number of basic charges found at the start of the N-terminal acidic domain of haloarchaeal FtsY proteins (the region of the protein thought to mediate FtsY,membrane association in Bacteria). Moreover, FtsY, but not the NG domain, was shown to mediate membrane association of H. volcanii SRP54, a protein that did not otherwise interact with the membrane. [source] Effects of modification of membrane lipid composition on Bacillus subtilis sporulation and spore propertiesJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2009K.K. Griffiths Abstract Aims:, To determine effects of inner membrane lipid composition on Bacillus subtilis sporulation and spore properties. Methods and Results:, The absence of genes encoding lipid biosynthetic enzymes had no effect on B. subtilis sporulation, although the expected lipids were absent from spores' inner membrane. The rate of spore germination with nutrients was decreased c. 50% with mutants that lacked the major cardiolipin (CL) synthase and another enzyme for synthesis of a major phospholipid. Spores lacking the minor CL synthase or an enzyme essential for glycolipid synthesis exhibited 50,150% increases in rates of dodecylamine germination, while spores lacking enzymes for phosphatidylethanolamine (PE), phosphatidylserine (PS) and lysylphosphatidylglycerol (l-PG) synthesis exhibited a 30,50% decrease. Spore sensitivity to H2O2 and tert-butylhydroperoxide was increased 30,60% in the absence of the major CL synthase, but these spores' sensitivity to NaOCl or OxoneÔ was unaffected. Spores of lipid synthesis mutants were less resistant to wet heat, with spores lacking enzymes for PE, PS or l-PG synthesis exhibiting a two to threefold decrease and spores of other strains exhibiting a four to 10-fold decrease. The decrease in spore wet heat resistance correlated with an increase in core water content. Conclusions:, Changing the lipid composition of the B. subtilis inner membrane did not affect sporulation, although modest effects on spore germination and wet heat and oxidizing agent sensitivity were observed, especially when multiple lipids were absent. The increases in rates of dodecylamine germination were likely due to increased ability of this compound to interact with the spore's inner membrane in the absence of some CL and glycolipids. The effects on spore wet heat sensitivity are likely indirect, because they were correlated with changes in core water content. Significance and Impact of the Study:, The results of this study provide insight into roles of inner membrane lipids in spore properties. [source] Endotoxin increases hepatic susceptibility to lipid peroxidation: A possible role of ironJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 1 2004W. Ibrahim Abstract The purpose of this study was to investigate the possible mechanism by which endotoxin enhances peroxidative damage to membrane lipids. Male B6C3 mice were treated with endotoxin intraperitoneally 0 or 20 mg/kg body weight for 24 h. Freshly prepared liver homogenate was incubated with either 1,5 mM of reduced glutathione (GSH), glucose, H2O2, ascorbic acid (AA), FeSO4, FeCl3, EDTA, FeCl3 plus AA, AA plus EDTA or EDTA plus FeCl3 in phosphate-buffered saline (PBS), pH 7.0, or PBS, at 37°C for 60 min. The levels of lipid peroxidation products, thiobarbituric acid reactants (TBAR), were significantly higher in the liver of endotoxin-treated mice, and the values were markedly increased following incubation. Compared to PBS, incubation with H2O2, FeCl3, FeSO4, and AA, but not glucose, significantly enhanced TBAR formation. The greatest increase of TBAR was found when AA and FeCl3 were added together. On the other hand, EDTA and GSH inhibited the formation of TBAR during incubation. When added before AA, EDTA completely inhibited the peroxidative effect of AA or FeSO4, and when added subsequent to AA, EDTA partially prevented the adverse effect of AA. The results obtained suggest that ionic iron plays an important role in initiating endotoxin-induced peroxidative damage to membrane lipids, and that AA may be involved in releasing iron from its protein complex and/or maintaining ionic iron in a reduced or catalytic state. © 2004 Wiley Periodicals, Inc. J Biochem Mol Toxicol 18:23,29, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20002 [source] Interactions Between Wine Lees and Polyphenols: Influence on Oxygen Consumption Capacity During Simulation of Wine AgingJOURNAL OF FOOD SCIENCE, Issue 5 2002J.M. Salmon ABSTRACT: During wine aging on lees, some membrane lipids of yeast lees, in contact with dissolved oxygen at low concentration, may undergo mild oxidation explaining the capacity of yeast lees to consume oxygen. We studied the cross-reactivity of complex polyphenols and tannins from wine and yeast lees towards oxygen during simulation of wine aging. We observed a total decrease of oxygen consumption capacity of mixed yeast lees and wine polyphenol by comparison with the reactivity of each component studied alone. A strong loss of reactivity of yeast lees towards oxygen was observed when separated from soluble polyphenols, although only a fraction of the total polyphenols remained adsorbed on lees. [source] The ,-amyloid protein of Alzheimer's disease binds to membrane lipids but does not bind to the ,7 nicotinic acetylcholine receptorJOURNAL OF NEUROCHEMISTRY, Issue 6 2007David H. Small Abstract Accumulation of the amyloid protein (A,) in the brain is an important step in the pathogenesis of Alzheimer's disease. However, the mechanism by which A, exerts its neurotoxic effect is largely unknown. It has been suggested that the peptide can bind to the ,7 nicotinic acetylcholine receptor (,7nAChR). In this study, we examined the binding of A,1-42 to endogenous and recombinantly expressed ,7nAChRs. A,1-42 did neither inhibit the specific binding of ,7nAChR ligands to rat brain homogenate or slice preparations, nor did it influence the activity of ,7nAChRs expressed in Xenopus oocytes. Similarly, A,1-42 did not compete for ,-bungarotoxin-binding sites on SH-SY5Y cells stably expressing ,7nAChRs. The effect of the A,1-42 on tau phosphorylation was also examined. Although A,1-42 altered tau phosphorylation in ,7nAChR-transfected SH-SY5Y cells, the effect of the peptide was unrelated to ,7nAChR expression or activity. Binding studies using surface plasmon resonance indicated that the majority of the A, bound to membrane lipid, rather than to a protein component. Fluorescence anisotropy experiments indicated that A, may disrupt membrane lipid structure or fluidity. We conclude that the effects of A, are unlikely to be mediated by direct binding to the ,7nAChR. Instead, we speculate that A, may exert its effects by altering the packing of lipids within the plasma membrane, which could, in turn, influence the function of a variety of receptors and channels on the cell surface. [source] Matrix formalism for site-specific binding of unstructured proteins to multicomponent lipid membranes,JOURNAL OF PEPTIDE SCIENCE, Issue 4 2008Vladimir B. Teif Abstract We describe a new approach to calculate the binding of flexible peptides and unfolded proteins to multicomponent lipid membranes. The method is based on the transfer matrix formalism of statistical mechanics recently described as a systematic tool to study DNA,protein,drug binding in gene regulation. Using the energies of interaction of the individual polymer segments with different membrane lipid species and the scaling corrections due to polymer looping, we calculate polymer adsorption characteristics and the degree of sequestration of specific membrane lipids. The method is applied to the effector domain of the MARCKS (myristoylated alanine rich C kinase substrate) protein known to be involved in signal transduction through membrane binding. The calculated binding constants of the MARCKS(151,175) peptide and a series of related peptides to mixed PC/PS/PIP2 membranes are in satisfactory agreement with in vitro experiments. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source] Effectiveness of Four New Pyrazole-pyrimidines on Phytopathogens: Ultrastructural Evidences on Pythium ultimumJOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2000D. Mares Four newly synthesized molecules derived from pyrazole-pyrimidine were assayed on Botrytis cinerea Micheli, Fusarium moniliforme Sheld and Pythium ultimum Trow. All proved effective in inhibiting the growth of the phytopathogens at all of the test concentrations (10, 20, 50, 100 ,g/ml). The most effective compound was 1-(3)nitrophenyl - 6 - trifluoromethylpyrazolo[3,4 - d]pyrimidine 4(5H)-thione (CF33). Ultrastructural studies on P. ultimum treated with CF33 revealed alterations in the normal hyphal shape and, at high concentration, plasmolysis and damage to the wall texture was observed. At 20 ,g/ml different vesicles were seen in the cytoplasm: some appeared quite dense, and specific cytochemical reactions indicated that they were most likely peroxysomes; other vesicles seem to be vacuoles of varying content. In some cases there was disintegration of the nuclear envelope. The effects on membrane lipids and interference in protein synthesis are hypothesized as possible mechanism of action of the molecule. Zusammenfassung Vier neu synthetisierte Pyrazol-Pyrimidin-Derivate wurden an Botrytis cinerea Micheli, Fusarium moniliforme Sheld und Pythium ultimum Trow. geprüft. Alle hemmten das Wachstum der Phytopathogene in allen Testkonzentrationen (10, 20, 50 und 100 ,g/ml). Die wirksamste Verbindung war 1-(3)Nitrophenyl-6-trifluormethylpyrazolo[3,4-d]pyrimidin-4(5H)-thion (CF33). Feinstrukturelle Untersuchungen an mit CF33 behandeltem P. ultimum zeigten Veränderungen in der normalen Hyphenform, bei hohen Konzentrationen wurden zudem Plasmolyse und Schäden der Wandstruktur beobachtet. Bei 20 ,g/ml waren verschiedene Vesikel im Cytoplasma zu sehen. Einige von diesen waren recht dicht, und spezifische cytochemische Reaktionen ergaben, dai es sich höchstwahrscheinlich um Peroxisomen handelte. Andere Vesikel waren offenbar Vakuolen unterschiedlichen Inhalts. In einigen Fällen kam es zur Auflösung der Kernmembran. Als mögliche Wirkungsmechanismen des Moleküls werden die Wirkungen auf die Membranlipide und der Eingriff in die Proteinsynthese angesehen. [source] Borrelia burgdorferi membranes are the primary targets of reactive oxygen speciesMOLECULAR MICROBIOLOGY, Issue 3 2008Julie A. Boylan Summary Spirochetes living in an oxygen-rich environment or when challenged by host immune cells are exposed to reactive oxygen species (ROS). These species can harm/destroy cysteinyl residues, iron-sulphur clusters, DNA and polyunsaturated lipids, leading to inhibition of growth or cell death. Because Borrelia burgdorferi contains no intracellular iron, DNA is most likely not a major target for ROS via Fenton reaction. In support of this, growth of B. burgdorferi in the presence of 5 mM H2O2 had no effect on the DNA mutation rate (spontaneous coumermycin A1 resistance), and cells treated with 10 mM t -butyl hydroperoxide or 10 mM H2O2 show no increase in DNA damage. Unlike most bacteria, B. burgdorferi incorporates ROS-susceptible polyunsaturated fatty acids from the environment into their membranes. Analysis of lipoxidase-treated B. burgdorferi cells by Electron Microscopy showed significant irregularities indicative of membrane damage. Fatty acid analysis of cells treated with lipoxidase indicated that host-derived linoleic acid had been dramatically reduced (50-fold) in these cells, with a corresponding increase in the levels of malondialdehyde by-product (fourfold). These data suggest that B. burgdorferi membrane lipids are targets for attack by ROS encountered in the various stages of the infective cycle. [source] A bacterium that has three pathways to regulate membrane lipid fluidityMOLECULAR MICROBIOLOGY, Issue 2 2006John E. Cronan Summary Well-studied bacteria such as Bacillus subtilis and Escherichia coli each have only a single pathway for synthesis of the unsaturated fatty acids required to make functional membrane lipids. In marked contrast, unsaturated fatty acid synthesis in Pseudomonas aeruginosa proceeds by three distinct pathways. [source] Changes in lipopolysaccharide structure induce the ,E -dependent response of Escherichia coliMOLECULAR MICROBIOLOGY, Issue 5 2005Christina Tam Summary The envelope of Escherichia coli is composed of an asymmetric lipid bilayer containing lipopolysaccharide, phospholipid and outer membrane proteins (OMPs). Physical and chemical stresses impact on the integrity of the outer membrane envelope and trigger the ,E -dependent response, whereby E. coli activates the expression of genes that increase its capacity for folding OMPs and synthesizing lipopolysaccharide (LPS). While it has already been appreciated that misfolded OMPs induce the ,E response, a role for LPS in activating this pathway was hitherto unknown. Here we show that ammonium metavandate (NH4VO3) induces multiple changes in E. coli LPS structure and activates the ,E -dependent response without altering OMP. One such NH4VO3 -mediated LPS decoration, the CrcA/PagP-catalysed addition of palmitate to lipid A, appeared to be alone sufficient to activate transcription at ,E -dependent promoters. Furthermore, reduced acylation of LPS, caused by htrB or msbB mutations, also resulted in a constitutive expression of the ,E regulon above wild-type levels. Production of these aberrant outer membrane lipids did not noticeably affect the composition or the amount of OMPs. A model is proposed whereby structural intermediates of the LPS biosynthetic pathway or modified LPS molecules may function as signals that activate the ,E response. [source] Non-growing Escherichia coli cells starved for glucose or phosphate use different mechanisms to survive oxidative stress,MOLECULAR MICROBIOLOGY, Issue 4 2001Patrice L. Moreau Recent data suggest that superoxide dismutases are important in preventing lethal oxidative damage of proteins in Escherichia coli cells incubated under aerobic, carbon starvation conditions. Here, we show that the alkylhydroperoxide reductase AhpCF (AHP) is specifically required to protect cells incubated under aerobic, phosphate (Pi) starvation conditions. Additional loss of the HP-I (KatG) hydroperoxidase activity dramatically accelerated the death rate of AHP-deficient cells. Investigation of the composition of spent culture media indicates that ,ahpCF katG cells leak nutrients, which suggests that membrane lipids are the principal target of peroxides produced in Pi-starved cells. In fact, the introduction of various mutations inactivating repair activities revealed no obvious role for protein or DNA lesions in the viability of ahp cells. Because the death of ahp cells was directly related to ongoing aerobic glucose metabolism, we wondered how glycolysis, which requires free Pi, could proceed. 31P nuclear magnetic resonance spectra showed that Pi-starved cells consumed Pi but were apparently able to liberate Pi from phosphorylated products, notably through the synthesis of UDP-glucose. Whereas expression of the ahpCF and katG genes is enhanced in an OxyR-dependent manner in response to H2O2 challenge, we found that the inactivation of oxyR and both oxyR and rpoS genes had little effect on the viability of Pi-starved cells. In stark contrast, the inactivation of both oxyR and rpoS genes dramatically decreased the viability of glucose-starved cells. [source] Cold adaptation in Arctic and Antarctic fungiNEW PHYTOLOGIST, Issue 2 2001Clare H. Robinson Summary Growth and activity at low temperatures and possible physiological and ecological mechanisms underlying survival of fungi isolated from the cold Arctic and Antarctic are reviewed here. Physiological mechanisms conferring cold tolerance in fungi are complex; they include increases in intracellular trehalose and polyol concentrations and unsaturated membrane lipids as well as secretion of antifreeze proteins and enzymes active at low temperatures. A combination of these mechanisms is necessary for the psychrotroph or psychrophile to function. Ecological mechanisms for survival might include cold avoidance; fungal spores may germinate annually in spring and summer, so avoiding the coldest months. Whether spores survive over winter or are dispersed from elsewhere is unknown. There are also few data on persistence of basidiomycete vs microfungal mycelia and on the relationship between low temperatures and the predominance of sterile mycelia in tundra soils. Acclimation of mycelia is a physiological adaptation to subzero temperatures; however, the extent to which this occurs in the natural environment is unclear. Melanin in dark septate hyphae, which predominate in polar soils, could protect hyphae from extreme temperatures and play a significant role in their persistence from year to year. [source] Novel Methyl Helianthrones as Photosensitizers: Synthesis and Biological Evaluation,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Shai Rahimipour ABSTRACT A combination of light, oxygen and a photosensitizer is used to induce death of cancer cells by photodynamic therapy. In this study, we have synthesized several new methyl helianthrone derivatives and compared their phototoxicity with that of hypericin. In contrast to hypericin, methyl helianthrones are soluble in aqueous solutions and have a broad range of light absorbance, which allows the use of polychromatic light. Structural modifications of methyl helianthrone demonstrated that substitution of hydrogen atoms of methyl helianthrone at Positions 2 and 5 with Br atoms or methylation of its phenolic hydroxyls, significantly increases the corresponding singlet oxygen quantum yield and their phototoxicity toward ,T3-1, M2R and LNCaP cells. The phototoxicity of some of these compounds was similar to that of hypericin. Methyl helianthrones, like hypericin, accumulated mainly in the perinuclear region as evident by confocal microscopy. Irradiation of cells pretreated with methyl helianthrone derivatives generates intracellular reactive oxygen species and lipid free radicals, as shown by a fluorescentic probe and electron paramagnetic resonance methods, respectively. The phototoxicity of these methyl helianthrones as well as their ability to oxidize membrane lipids were significantly decreased on addition of specific Type-II inhibitors, suggesting the involvement of singlet oxygen as the main oxidant. [source] Self-sensitized Photodegradation of Membrane-bound Protoporphyrin Mediated by Chain Lipid Peroxidation: Inhibition by Nitric Oxide with Sustained Singlet Oxygen DamagePHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Magdalena Niziolek ABSTRACT In the presence of exciting light, iron and reductants, the singlet oxygen (1O2)-generating sensitizer protoporphyrin IX (PpIX) induces free radical lipid peroxidation in membranes, but gradually degrades in the process. We postulated that NO, acting as a chain-breaking antioxidant, would protect PpIX against degradation and consequently prolong its ability to produce 1O2. This idea was tested by irradiating PpIX-containing liposomes (LUVs) in the presence of iron and ascorbate, and monitoring the cholesterol hydroperoxides 5,-OOH and 7,/,-OOH as respective 1O2 and free radical reporters. 5,-OOH accumulation, initially linear with light fluence, slowed progressively after prolonged irradiation, whereas 7,/,-OOH accumulation only accelerated after an initial lag. The active, but not spent, NO donor spermine NONOate (0.4 mM) virtually abolished 7,/,-OOH buildup as well as 5,-OOH slowdown. Increasing membrane phospholipid unsaturation hastened the onset of rapid chain peroxidation and 5,-OOH slowdown. Accompanying the 5,-OOH effect was a steady decrease in 1O2 quantum yield and PpIX fluorescence at 632 nm, both of which were inhibited by NO. An NO-inhibitable decay of PpIX fluorescence was also observed during dark incubation of 5,-OOH-bearing LUVs with iron and ascorbate, confirming a link between chain peroxidation and PpIX loss. By protecting PpIX in irradiated membranes, NO might select for and prolong purely 1O2 -mediated damage. Supporting this was our observation that 1O2 -mediated photoinactivation of a nonmembrane target, lactate dehydrogenase, slowed concurrently with 5,-OOH accumulation and that spermine NONOate prevented this. Thus, NO not only protected membrane lipids against PpIX-sensitized free radical damage, but PpIX itself, thereby extending its 1O2 -generating lifetime. Consistent findings were obtained using porphyrin-sensitized COH-BR1 cells. These previously unrecognized effects of NO could have important bearing on 5-aminolevulinate-based photodynamic therapy in which PpIX is metabolically deposited in tumor cells. [source] The chloroplastic lipocalin AtCHL prevents lipid peroxidation and protects Arabidopsis against oxidative stressTHE PLANT JOURNAL, Issue 4 2009Gabriel Levesque-Tremblay Summary Lipocalins are small ligand-binding proteins with a simple tertiary structure that gives them the ability to bind small, generally hydrophobic, molecules. Recent studies have shown that animal lipocalins play important roles in the regulation of developmental processes and are involved in tolerance to oxidative stress. Plants also possess various types of lipocalins, and bioinformatics analyses have predicted that some lipocalin members may be present in the chloroplast. Here we report the functional characterization of the Arabidopsis thaliana chloroplastic lipocalin AtCHL. Cellular fractionation showed that AtCHL is a thylakoid lumenal protein. Drought, high light, paraquat and abscisic acid treatments induce AtCHL transcript and protein accumulation. Under normal growth conditions, knockout (KO) and over-expressing (OEX) lines do not differ from wild-type plants in terms of phenotype and photosynthetic performance. However, KO plants, which do not accumulate AtCHL, show more damage upon photo-oxidative stress induced by drought, high light or paraquat. In contrast, a high level of AtCHL allows OEX plants to cope better with these stress conditions. When exposed to excess light, KO plants display a rapid accumulation of hydroxy fatty acids relative to the wild-type, whereas the lipid peroxidation level remains very low in OEX plants. The increased lipid peroxidation in KO plants is mediated by singlet oxygen and is not correlated with photo-inhibition of the photosystems. This work provides evidence suggesting that AtCHL is involved in the protection of thylakoidal membrane lipids against reactive oxygen species, especially singlet oxygen, produced in excess light. [source] Metabolomic approaches reveal that phosphatidic and phosphatidyl glycerol phospholipids are major discriminatory non-polar metabolites in responses by Brachypodium distachyon to challenge by Magnaporthe griseaTHE PLANT JOURNAL, Issue 3 2006J. William Allwood Summary Metabolomic approaches were used to elucidate some key metabolite changes occurring during interactions of Magnaporthe grisea, the cause of rice blast disease , with an alternate host, Brachypodium distachyon. Fourier-transform infrared (FT-IR) spectroscopy provided a high-throughput metabolic fingerprint of M. grisea interacting with the B. distachyon accessions ABR1 (susceptible) and ABR5 (resistant). Principal component,discriminant function analysis (PC-DFA) allowed the differentiation between developing disease symptoms and host resistance. Alignment of projected ,test-set' on to ,training-set' data indicated that our experimental approach produced highly reproducible data. Examination of PC-DFA loading plots indicated that fatty acids were one chemical group that discriminated between responses by ABR1 and ABR5 to M. grisea. To identify these, non-polar extracts of M. grisea -challenged B. distachyon were directly infused into an electrospray ionization mass spectrometer (ESI-MS). PC-DFA indicated that M. grisea -challenged ABR1 and ABR5 were differentially clustered away from healthy material. Subtraction spectra and PC-DFA loadings plots revealed discriminatory analytes (m/z) between each interaction and seven metabolites were subsequently identified as phospholipids (PLs) by ESI-MS-MS. Phosphatidyl glycerol (PG) PLs were suppressed during both resistant and susceptible responses. By contrast, different phosphatidic acid PLs either increased or were reduced during resistance or during disease development. This suggests considerable and differential PL processing of membrane lipids during each interaction which may be associated with the elaboration/suppression of defence mechanisms or developing disease symptoms. [source] The effect of phenyltin chlorides on osmotically induced erythrocyte haemolysisAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2005Adam Miszta Abstract The toxicity of many amphiphilic compounds may result from their effect on the lipid phase of biological membranes. Upon incorporation such compounds may change the properties of membranes in general and in particular alter the organization of membrane lipids. These changes should affect, among other things, the mechanical properties of membranes. We selected two amphiphilic compounds, diphenyltin dichloride (Ph2SnCl2) and triphenyltin chloride (Ph3SnCl), which are known to be located at different regions of the lipid bilayer and to be toxic. As a model biological membrane the erythrocyte plasma membrane was used. Analysis of the haemolysis kinetics showed differences between the effect of the compound studied on mechanical properties at so-called non-lytic concentrations. Diphenyltin dichloride showed a limited effect on erythrocyte haemolysis, whereas triphenyltin chloride affected all the parameters measured (extent of initial haemolysis, extent of final haemolysis and membrane mechanical strength). We correlated these effects with the location of the investigated compounds in liposomes. The presented data show that triphenyltin chloride reduces the erythrocyte plasma membrane mechanical strength and increases the extent of haemolysis under osmotic stress conditions. Copyright © 2005 John Wiley & Sons, Ltd. [source] Antioxidative and Prooxidative Action of Stilbene DerivativesBASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 5 2000Toshiaki Miura The effects of stilbene derivatives, including resveratrol, diethylstilboestrol and stilbene, as antioxidants or prooxidants were examined. Resveratrol and diethylstilboestrol, but not stilbene, strongly inhibited NADPH- and adenosine 5,-diphosphate (ADP)-Fe3+ -dependent lipid peroxidation at the initial and propagation stages. In addition, phenolic stilbenes also inhibited ultraviolet light-induced lipid peroxidation. Resveratrol and diethylstilboestrol efficiently scavenged 2,2,-azobis-(2-amidinopropane)-dihydrochloride peroxyl radicals. However, 2,2,-diphenyl-p-picrylhydrazyl radicals were trapped only by resveratrol, but not by diethylstilboestrol. These results suggest that the inhibitory effect of phenolic stilbenes on lipid peroxidation was due to their scavenging ability of lipid peroxyl and/or carbon-cantered radicals. Resveratrol efficiently reduced ADP-Fe3+, but not EDTA-Fe3+. Stilbenes and diethylstilboestrol did not reduce either ADP-Fe3+ or EDTA-Fe3+. The strand breaks of DNA were stimulated during the interaction of resveratrol with ADP-Fe3+ in the presence of H2O2. These results suggest that phenolic stilbenes act as antioxidants of membrane lipids and that resveratrol has a prooxidative effect DNA damage during interaction with ADP-Fe3+ in the presence of H2O2. [source] The evolution of coenzyme QBIOFACTORS, Issue 1-4 2008Frederick L. Crane In the 50 years since the identification of coenzyme Q as an electron carrier in mitochondria, it has been identified with diverse and unexpected functions in cells. Its discovery came as a result of a search for electron carriers in mitochondria following the identification of flavin and cytochromes by Warburg, Keilin, Chance and others. As a result of investigation of membrane lipids at D.E. Green's laboratory at University of Wisconsin coenzyme Q was identified as the electron carrier between primary flavoprotein dehydrogenases and the cytochromes. Then Peter Mitchell identified the role of transmembrane proton transfer as a basis for ATP synthesis. The general distribution of coenzyme Q in all cell membranes then led to the recognition of a role as a primary antioxidant. The protonophoric function was extended to acidification of Golgi and lysosomal vericles. A further role in proton release through the plasma membrane and its relation to cell proliferation has not been fully developed. A role in generation of H2 O2 as a messenger for hormone and cytokine action is indicated as well as prevention of apoptosis by inhibition of ceramide release. Identification of the genes and proteins required for coenzyme Q synthesis has led to a basis for defining deficiency. For 50 years Karl Folkers has led the search for deficiency and therapeutic application. The development of large scale production, better formulation for uptake, and better methods for analysis have furthered this search. The story isn't over yet. Questions remain about effects on membrane structure, breakdown and control of cellular synthesis and uptake and the basis for therapeutic action. [source] Protective effects of N-acetyl- L -cysteine against acute carbon tetrachloride hepatotoxicity in ratsCELL BIOCHEMISTRY AND FUNCTION, Issue 1 2008Yu. Z. Maksimchik Abstract In recent years, N-acetyl- L -cysteine (NAC) has been widely investigated as a potentially useful protective and antioxidative agent to be applied in many pathological states. The aim of the present work was further evaluation of the mechanisms of the NAC protective effect under carbon tetrachloride-induced acute liver injuries in rats. The rat treatment with CCl4 (4,g/kg, intragastrically) caused pronounced hepatolysis observed as an increase in blood plasma bilirubin levels and hepatic enzyme activities, which agreed with numerous previous observations. The rat intoxication was accompanied by an enhancement of membrane lipid peroxidation (1.4-fold) and protein oxidative damage (protein carbonyl group and mixed protein-glutathione disulphide formations) in the rat liver. The levels of nitric oxide in blood plasma and liver tissue significantly increased (5.3- and 1.5-fold, respectively) as blood plasma triacylglycerols decreased (1.6-fold). The NAC administration to control and intoxicated animals (three times at doses of 150,mg/kg) elevated low-molecular-weight thiols in the liver. The NAC administration under CCl4 -induced intoxication prevented oxidative damage of liver cells, decreased membrane lipid peroxidation, protein carbonyls and mixed protein-glutathione disulphides formation, and partially normalized plasma triacylglycerols. At the same time the NAC treatment of intoxicated animals did not produce a marked decrease of the elevated levels of blood plasma ALT and AST activities and bilirubin. The in vitro exposure of human red blood cells to NAC increased the cellular low-molecular-weight thiol levels and retarded tert -butylhydroperoxide-induced cellular thiol depletion and membrane lipid peroxidation as well as effectively inhibited hypochlorous acid-induced erythrocyte lysis. Thus, NAC can replenish non-protein cellular thiols and protect membrane lipids and proteins due to its direct radical-scavenging properties, but it did not attenuate hepatotoxicity in the acute rat CCl4 -intoxication model. Copyright © 2007 John Wiley & Sons, Ltd. [source] Structural Diversity of PDZ,Lipid InteractionsCHEMBIOCHEM, Issue 4 2010Rodrigo Gallardo Abstract PDZ domains are globular protein modules that are over-and-above appreciated for their interaction with short peptide motifs found in the cytosolic tail of membrane receptors, channels, and adhesion molecules. These domains predominate in scaffold molecules that control the assembly and the location of large signaling complexes. Studies have now emerged showing that PDZ domains can also interact with membrane lipids, and in particular with phosphoinositides. Phosphoinositides control various aspects of cell signaling, vesicular trafficking, and cytoskeleton remodeling. When investigated, lipid binding appears to be extremely relevant for PDZ protein functionality. Studies point to more than one mechanism for PDZ domains to associate with lipids. Few studies have been focused on the structural basis of PDZ,phosphoinositide interactions, and the biological consequences of such interactions. Using the current knowledge on syntenin-1, syntenin-2, PTP-Bas, PAR-3 and PICK1, we recapitulate our understanding of the structural and biochemical aspects of PDZ,lipid interactions and the consequences for peptide interactions. [source] Structural Features of Interacting Complementary Liposomes Promoting Formation of Multicompartment StructuresCHEMPHYSCHEM, Issue 17 2009Zili Sideratou Dr. Abstract The structural features of complementary liposomes and factors favoring formation of multicompartment systems are investigated. Specifically, liposomal formulations consisting of PEGylated unilamellar liposomes with guanidinium moieties located at the distal end of polyethylene glycol (PEG) chains interact with complementary multilamellar liposomes bearing phosphate moieties. Furthermore, the number of PEG chains attached to the unilamellar interface of the liposomes is enhanced by incorporating PEGylated cholesterol in their bilayer. While molecular recognition of the liposomes is the driving force for initiating multicompartmentalization, it is the enhanced PEGylation at the liposomal interface that synergistically promotes fusion resulting in large and well-formed multicompartment systems. A mechanism is proposed according to which initial adhesion of the liposomes, followed by reorganization of their membrane lipids, leads to giant bilayer aggregates incorporating large liposomes. [source] | ||||||||||||||||